Silicon substrates are widely used in the manufacture of semiconductor devices. Low cost and highly evolved manufacturing techniques make Silicon a preferred material in many applications, when compared with other semiconductor materials. Standard complementary metal oxide semiconductor (CMOS) process techniques are often used with Silicon and are highly evolved and cost effective. High resistivity Silicon substrates may be used in radio frequency (RF) devices. If the period of an RF signal is shorter than a majority carrier relaxation time, then the majority carriers in a Silicon substrate may not respond to the RF signal. The majority carriers may appear to be frozen and the Silicon substrate may behave as a dielectric. However, Silicon has certain characteristics that may produce undesirable behavior in some RF applications.
For example, the doping level in high resistivity Silicon is very low or non-existent; therefore, oxide charges at the surface of a Silicon substrate, or a weak electric field in the Silicon substrate, can induce an inversion or accumulation layer, which may function as a surface conduction layer at the surface of the Silicon substrate. RF signals traversing above the surface of the Silicon substrate may modulate the surface conduction layer, which may cause non-linear capacitance, non-linear conductance, or both affecting RF interactions between the Silicon substrate and other layers. The non-linear characteristics may introduce harmonic distortion in the RF signals, which may exceed allowable limits.
One technique for reducing the impact of the non-linear characteristics is to incorporate a conductive shielding layer between the surface of the Silicon substrate and other layers handling RF signals; however, the conductive shielding layer may increase complexity and signal loss. Thus, there is a need to reduce, or eliminate, non-linear characteristics associated with a surface conduction layer without using a conductive shielding layer using standard CMOS process techniques.